merge_sort.py

# Python program for implementation of MergeSort 
  
def merge(arr, l, m, r): 
    n1 = m - l + 1
    n2 = r- m 
  
    L = [0] * (n1) 
    R = [0] * (n2) 
  
    for i in range(0 , n1): 
        L[i] = arr[l + i] 
  
    for j in range(0 , n2): 
        R[j] = arr[m + 1 + j] 
    i = 0      
    j = 0
    k = l     
  
    while i < n1 and j < n2 : 
        if L[i] <= R[j]: 
            arr[k] = L[i] 
            i += 1
        else: 
            arr[k] = R[j] 
            j += 1
        k += 1
    while i < n1: 
        arr[k] = L[i] 
        i += 1
        k += 1
  
    while j < n2: 
        arr[k] = R[j] 
        j += 1
        k += 1
  
def mergeSort(arr,l,r): 
    if l < r: 
  
        m = (l+(r-1))//2
  
        mergeSort(arr, l, m) 
        mergeSort(arr, m+1, r) 
        merge(arr, l, m, r) 
  
  
arr = [12, 11, 13, 5, 6, 7] 
n = len(arr) 
print ("Given array is") 
for i in range(n): 
    print ("%d" %arr[i]), 
  
mergeSort(arr,0,n-1) 
print ("\n\nSorted array is") 
for i in range(n): 
    print ("%d" %arr[i]),